Which rotor sirens most efficient? (Most dB/watt)

[Robert Gift]

Has anyone ever done a comparison of sirens' efficiencies compared to one another?

Such as how many dB/watt?
Or dB/horsepower?

I suspect that FedSig 2001 is most dB/watt.
Allerter, least, because it's donut ring around the stator
may block or cancel too much sound.

TOTAL of all motors; rotor, compressor, rotater.

Thank you,

[SirenMadness]

At a hundred feet away from itself, the 2001 SRN-B is the best, because a high pitch has a higher pressure in a specific space, than a lower-pitch siren, such as a T-128, assuming that you pump the same amount of energy to each type of wave; the higher the pitch, the higher the concentration of the waves. However, at a long distance, the rotor of the T-128 would perform more efficiently, because you let the length and lower pressure do the work, by cutting through the air easier. In contrast, it is also probably the high pressure of higher pitches that reduces their length of travel, because of the resistance that is caused by the pressure of the sound against the medium of conducting.

[Brendan Ahern]

Not sure about wattage or amperage of every unit, but generally, the more voltage, the less wattage. But in respect to horsepower the 2001 is probably the most efficient. Its 6.5 horsepower. 6 for the rotor and half for rotation. The tbolt has a 2 hp chopper and a 1/3 hp rotator, but then again it does have a 10 hp blower. Then you have the allertor which is 10 hp for both sound and rotation. And it puts out 125db. Least efficient would obviously be the t-135 and most sentrys. Look at the 40V2T, it is rated at 127db @ 100 ft. Look at the 2001, 128 db @ 100 ft. Yet the 40V2T is rated at 40 hp. But really and truly, not trying to knock your question at all, but its all pretty much a moot point. The fact is, how long and often do any sirens run? Its not a continuous duty machine. You figure 3 mins or so at a time. A weekly or monthly test and in an emergency. Take Chicago for example. The system has never been used, just tested. So from 1998 to now the only activation its seen is a weekly silent polling where it rotates, and a monthly test. You figure the rotator test takes about 10 seconds and the main monthly is timed at around 30 seconds give or take a few. so that means that in 8 years total run time has been 48 minutes for the siren head and 118 minutes for the rotator. Thats less than 2 hours in 8 years!

[Robert Gift]

Not sure about wattage or amperage of every unit, but generally, the more voltage, the less wattage. But in respect to horsepower the 2001 is probably the most efficient. Its 6.5 horsepower. 6 for the rotor and half for rotation. The tbolt has a 2 hp chopper and a 1/3 hp rotator, but then again it does have a 10 hp blower. Then you have the allertor which is 10 hp for both sound and rotation. And it puts out 125db. Least efficient would obviously be the t-135 and most sentrys. Look at the 40V2T, it is rated at 127db @ 100 ft. Look at the 2001, 128 db @ 100 ft. Yet the 40V2T is rated at 40 hp. But really and truly, not trying to knock your question at all, but its all pretty much a moot point. The fact is, how long and often do any sirens run? Its not a continuous duty machine. You figure 3 mins or so at a time. A weekly or monthly test and in an emergency. Take Chicago for example. The system has never been used, just tested. So from 1998 to now the only activation its seen is a weekly silent polling where it rotates, and a monthly test. You figure the rotator test takes about 10 seconds and the main monthly is timed at around 30 seconds give or take a few. so that means that in 8 years total run time has been 48 minutes for the siren head and 118 minutes for the rotator. Thats less than 2 hours in 8 years!

I'm just trying to figure what is the best design.
The one which loses the least sound energy because of design deficiencies.

For example: FedSig's eQ electronic siren is 200 watts (2 100 watt drivers opposed in a box with outside grill. Supposedly the loudest electronic siren and sounds like the real Q2b.)

I believe our 200 watt Unitrol is louder. We have two 100W speakers. Each is a more efficient reentrant exponentially flared horn.
Much better than a "box" with a decorative grill possibly reflecting sound
waves and causing some cancelations.

I think many real sirens could be louder if sound wave cancelation problems and wave blockages were better handled.
I am amazed that the Allerter works as well as it does - if it does.

[Hacksaw]

I am amazed that the Allerter works as well as it does, if it does.

Oh, it does, it does. A Reporter a few years ago on The Weather Channel had to shout to be heard over an Allertor going off a block away during a Tornado Warning. Yes, I don't get how it avoids wave cancellation either.

[Robert Gift]

I'd like to remove the intake side half of that ring to see if the Allerter
would be even louder.
The remaining motor side half of that ring may act as a reflector.

[jkvernon]

Wouldn't that basically be a P-10/15? Or do you mean remove the whole front housing? I came across a picture of one once, I'll have to look for it though.

[cdvtripleseven]

Yes, I don't get how it avoids wave cancellation either.

Why would the waves cancel? Doesn't the air pulse out of all the ports
of the stator at the same time. Wouldn't pulses have to be out
of phase to cancel the pulses coming out of the stator?

[Nelso90]

Look at the distance the sound coming out the top goes, compared to the sound coming out the bottom. That would cause some out-of-phase waves, because of the slight time delay of the waves hitting the open atmosphere. But, I don't think it's enough to make a difference. But, what would make even more of a difference, is the effect that 2 tones mixing together makes. Instead of one pure wave, you have 2 different waves. Inherently, they will cancel each other out somewhere in the waveform. Am I right?

[SirenMadness]

Yeah, I think so; I think that the lower the pitch, the more cancellation you will actually have, because lower waves are very "unorganized," compared to higher waves. But even with a high pitch in one cone, yeah, the lower wave is bound to hunt it down at some point. So, a 2T22 or 3T22 or an STH-10 would perform with good efficiency.